Validity of the Weil-Felix test in the diagnosis of acute rickettsial infections in Sri Lanka.

The diagnosis of rickettsial infections in developing countries is based on clinical features and a positive Weil-Felix test (WFT), as tests such as indirect immunofluorescent antibody (IFA) assays are not available for routine use. We estimated the sensitivity of the WFT in Sri Lanka using IFA testing as the gold standard. The WFT demonstrated low sensitivity (33%) in diagnosing acute rickettsial infections and low specificity, with a positive titre of 1:320 seen in 54% of healthy volunteers and 62% of non-rickettsial fever patients. Therefore, the use of the WFT should be discouraged in the diagnosis of acute rickettsial infections.